stable is not the only release that debian offers,
Did you mean to say “branch” rather than “release”? Debian only releases stable. Everything else is part of the process of preparing and supporting stable.
Testing branch may work well or it may not. Its goal is to refine packages for the next stable release so it has an inherent strive towards quality, but it doesn’t have a commitment to “quality now” like stable does, just to “quality eventually”.
Testing’s quality is highest towards the start of each release cycle when it picks up from the previous stable release and towards the end when it’s getting ready to become the next stable. But the cycle is 2 years long.